Paul, it has been several months since I have written any code for the 12
bit ADC in the 148/149. However, I have vague recollections of having
similar problems to what you describe. However, (at least for me) it was due
to the way I initialised the consecutive channel capture. (Once again, this
was several months ago. So I cannot remember exactly what I was doing
wrong!) It took several rereads of the TI documentation to finally fully
absorb what was being said! I vaguely remember there was a bug in the
header file for the ADC as well! (Long since been fixed though. Unless it
has crept back in.)
Anyway, the following fragments are from my initialisation of the
ADC.(Partially hacked to get rid of stuff you wouldn't be interested in.
(RequiredChannels actually came from a structure.)
The whole thing easily ran at 40khz with no problems.
void SetupADC(void)
{
unsigned char *ADC_MCTL_X = (unsigned char *) 0x0080; // position of first
ADCMCTLx channel memory
int ChannelCnt;
ADC12CTL0 = ADC12ON | SHT1_1 | SHT0_1 | REF2_5V | REFON; // ADC on,
int. ref. on (2.5 V), sample timer = 2*4*250ns = 2uS (well within spec),
Encoding is OFF
ADC12CTL1 = ADC12SSEL_2 | ADC12DIV_1 | CSTARTADD_0 | CONSEQ_3 | SHP |
SHS_2; // MCLK / 2 = 4 MHz, sequence of channels run once!,
// Start a adcmem12 = 0, conversion initiated by Timer Bout.0
for (ChannelCnt = 0; ChannelCnt < (RequiredChannels - 1); ChannelCnt++)
//set up the group of ADC mems for the current conversion)
{
*(ADC_MCTL_X++) = SREF_1 | INCH_0; // int. ref., channel 0
}
*(ADC_MCTL_X) = EOS | SREF_1 | INCH_0; // int. ref., channel 0
ADC12IE = 0x0001 << ChannelCnt; // Interrupt when
conversion placed in
last used ADC12MEMx
}
Incidentally, the above shows a single channel being sampled multiple times.
To change this to an ad-hoc channel sequence would be trivial
I used the hardware multiplier in the ADC interrupt routine to MAC the
values, and also to shift the values, as I really only want the most
significant byte of data
The reading of the ADC from within an interrupt was trivial, no special
action required.
Hope this is helpful.
Cheers
Harry
-----Original Message-----
From: mspgcc-users-ad...@lists.sourceforge.net
[mailto:mspgcc-users-ad...@lists.sourceforge.net]on Behalf Of Paul Burke
Sent: Friday, April 11, 2003 1:49 AM
To: mspgcc-users
Subject: [Mspgcc-users] A Really Weird ADC12 Problem
Friends, Russians and Countrymen!
I have a problem which is seriously weird. (no, not that one, I've seen
the doctor about that).
This doesn't seem to be a GCC bug, so relax..
I have an F148 program in which a fair amount is going on: interrupts
for Timer_A0 and Port 2 edge (for a TimerA uart), Timer_A1 CCR1 and
CCR2, and receive interrupts for both hardware uarts.
All interrupt routines are enablenested, and the right code seems to be
generated. So far so good.
Now the problem: I am using the ADC in sequence mode, for a sequence of
six channels. I've tested this in a standalone program, it's fine. The
problem is, when I integrate it with my real program, the TimerA uart
hangs.
The ADC conversion is called from the CCR1/2 interrupt. CCR2 is the 1ms
timebase.
The odd part is, that if I jimmy the check for ADC ready test to always
return 1, everything works OK (except of course for the ADC). With the
ADC test in place, the CCR2 interrupt completes (so the ADC isn't
hanging), but the uart runs (sometimes for one or two characters,
sometimes for a couple of dozen) then hangs.
The ADC ready test (ADC12CTL0 & ADC12SC) seems to produce the right
code, and there's nothing else in that routine apart from the pushes and
pops. There are no extra pushes compared to when I make the routine
return TRUE, so I'm not running out of stack.
I'm baffled. Can I put it to your combined almost infinite brain power
to come up with an explanation?
Regards
Paul Burke
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